The present invention relates generally to gas turbine engine augmentors, and, more particularly, to an improved augmentor liner requiring reduced amounts of cooling airflow and having improved screech suppression means.
Gas turbine engine augmentors including cooling liners therefor are known in the art. Various types of cooling liners are known which perform at various levels of efficiency. However, a cooling liner should be effective at least for shielding the structural augmentor casing from hot augmentor combustion gases, for providing cooling air to an exhaust nozzle disposed at the downstream end of the augmentor and for providing screech suppression in the augmentor.
Screech is a term known in the art which is simply defined as intense combustion induced, high-frequency pressure oscillations which, under certain conditions, are generated in the augmentor. See, for example, U.S. Pat. No. 3,041,836--J. C. Truman et al, "Means for Eliminating Screech in Jet Propulsion Systems," which is assigned to the present assignee and is incorporated herein by reference. Uncontrolled screech reduces the high-cycle fatigue life of the augmentor due to primarily three modes of screech-induced vibration including radial, circumferential, and axial modes, and combinations thereof.
Preferably, the augmentor cooling liner should provide casing thermal shielding and maintain acceptable levels of metal temperature consistent with durability and life requirements for the augmentor, while utilizing the least possible amount of engine cooling air.
More specifically, augmentor combustion efficiency is directly proportional to the amount of discharge gases available from the gas turbine engine. Accordingly, any engine discharge gases, fan bypass air, for example, utilized for cooling the augmentor liner and not used in the augmentor combustion process, decreases augmentor temperature capability and efficiency. It therefore becomes apparent that reducing the amount of cooling air required in the augmentor correspondingly increases augmentor efficiency.
However, augmentors are generally long structures when compared to engine size and must accommodate relatively high combustion gas temperatures, both of these conditions requiring a substantial amount of cooling air. Known in the art are gas turbine engine augmentors utilizing relatively highly effective film-cooling structures, such as are found in engine combustors. Film cooling is typically provided by circumferential film-cooling nuggets having slots which are placed in relatively close axial positions so that film-cooling effectiveness is maintained relatively high from one slot to the next.
Also known in the art are augmentors employing convection-cooled liners. However, convection-cooled liners are not as efficient as film-cooled liners and although they may utilize less cooling air, they are not suitably effective in advanced augmentors having relatively high combustion temperatures.
Augmentors also typically include some form of screech suppression means. For example, it is known to utilize a relatively high density of small holes in the forward section of a liner near the augmentor flameholder for suppressing screech. However, in one embodiment, these screech holes communicate with an augmentor bypass duct defined between an outer casing and the liner, and, therefore, result in leakage of cooling air through these holes into the augmentor. Although this leaking cooling air is effective for cooling the screech suppression means of the liner, it is less effective than film-cooling slots.
Accordingly, it is an object of the present invention to provide a new and improved gas turbine engine augmentor.
Another object of the present invention is to provide a new and improved augmentor liner requiring reduced amounts of cooling air for improving augmentor operating performance and efficiency.
Another object of the present invention is to provide an augmentor liner which more effectively apportions and utilizes available cooling air.
Another object of the present invention is to provide a new and improved augmentor liner having improved screech suppression means.